<script type="text/javascript">
  // JavaScript code here
</script>

<script src="filename.js"></script>

setTimeout(function() {
  // code to execute after 1 second
}, 1000);

function addNumbers(a, b) {
  return a + b;
}
x = addNumbers(1, 2);

document.getElementById("elementID").innerHTML = "Hello World!";

console.log(a);              // write to the browser console
document.write(a);               // write to the HTML
alert(a);                       // output in an alert box
confirm("Really?");              // yes/no dialog, returns true/false
prompt("Your age?", "0");         // input dialog

/* Multi line
comment */
// One line comment

for (var i = 0; i < 10; i++) {
  document.write(i + ": " + i * 3 + "<br />");
}

var sum = 0;
for (var i = 0; i < a.length; i++) {
  sum += a[i];
}

var html = "";
for (var i of custOrder) {
  html += "<li>" + i + "</li>";
}

var i = 1;
while (i < 100) {
  i *= 2;
  document.write(i + ", ");
}

var i = 1;
do {
  i *= 2;
  document.write(i + ", ");
} while (i < 100);

for (var i = 0; i < 10; i++) {
  if (i == 5) { break; }
  document.write(i + ", ");
}

for (var i = 0; i < 10; i++) {
  if (i == 5) { continue; }
  document.write(i + ", ");
}

if ((age >= 14) && (age < 19)) {
  status = "Eligible.";
} else {
  status = "Not eligible.";
}

switch (new Date().getDay()) {
  case 6:
    text = "Saturday";
    break;
  case 0:
    text = "Sunday";
    break;
  default:
    text = "Whatever";
}

var a;                           // variable
var b = "init";                  // string
var c = "Hi" + " " + "Joe";      // = "Hi Joe"
var d = 1 + 2 + "3";             // = "33"
var e = [2, 3, 5, 8];               // array
var f = false;                   // boolean
var g = /()/;                    // RegEx
var h = function() {};            // function object
const PI = 3.14;                 // constant
var a = 1, b = 2, c = a + b;     // one line
let z = 'zzz';                   // block scope local variable

"use strict";   // Use strict mode to write secure code
x = 1;          // Throws an error because variable is not declared

false, true                      // boolean
18, 3.14, 0b10011, 0xF6, NaN    // number
"flower", 'John'                 // string
undefined, null, Infinity      // special

a = b + c - d;      // addition, subtraction
a = b * (c / d);    // multiplication, division
x = 100 % 48;        // modulo. 100 / 48 remainder = 4
a++; b--;            // postfix increment and decrement

a * (b + c)         // grouping
person.age          // member
person[age]         // member
!(a == b)           // logical not
a != b              // not equal
typeof a            // type (number, object, function...)
x << 2  x >> 3      // binary shifting
a = b               // assignment
a == b              // equals
a != b              // unequal
a === b             // strict equal
a !== b             // strict unequal
a < b   a > b       // less and greater than
a <= b  a >= b      // less or equal, greater or eq
a += b              // a = a + b (works with - * %...)
a && b              // logical and
a || b              // logical or

var age = 18;                            // number
var name = "Jane";                       // string
var name = {first: "Jane", last: "Doe"};  // object
var truth = false;                       // boolean
var sheets = ["HTML", "CSS", "JS"];       // array
var a; typeof a;                         // undefined
var a = null;                            // value null

var student = {                  // object name
  firstName: "Jane",           // list of properties and values
  lastName: "Doe",
  age: 18,
  height: 170,
  fullName: function() {     // object function
    return this.firstName + " " + this.lastName;
  }
};

student.age = 19;           // setting value
student[age]++;             // incrementing
name = student.fullName();  // call object function

var abc = "abcdefghijklmnopqrstuvwxyz";
var esc = 'I don\'t \n know';   // \n new line
var len = abc.length;           // string length
abc.indexOf("lmno");            // find substring, -1 if doesn't contain
abc.lastIndexOf("lmno");        // last occurrence
abc.slice(3, 6);                // cuts out "def", negative values count from behind
abc.replace("abc", "123");       // find and replace, takes regular expressions
abc.toUpperCase();              // convert to upper case
abc.toLowerCase();              // convert to lower case
abc.concat(" ", str2);          // abc + " " + str2
abc.charAt(2);                  // character at index: "c"
abc[2];                         // unsafe, abc[2] = "C" doesn't work
abc.charCodeAt(2);              // character code at index: "c" -> 99
abc.split(",");                 // splitting a string on commas gives an array
abc.split("");                  // splitting on characters
128.toString(16);               // number to hex(16), octal (8) or binary (2)

<button onclick="myFunction();">
Click here
</button>

var pi = 3.141;
pi.toFixed(0);          // returns 3
pi.toFixed(2);          // returns 3.14 - for working with money
pi.toPrecision(2);       // returns 3.1
pi.valueOf();           // returns number
Number(true);           // converts to number
Number(new Date());      // number of milliseconds since 1970
parseInt("3 months");   // returns the first number: 3
parseFloat("3.5 days"); // returns 3.5
Number.MAX_VALUE;       // largest possible JS number
Number.MIN_VALUE;       // smallest possible JS number
Number.NEGATIVE_INFINITY; // -Infinity
Number.POSITIVE_INFINITY; // Infinity

var pi = Math.PI;       // 3.141592653589793
Math.round(4.4);        // = 4 - rounded
Math.round(4.5);        // = 5
Math.pow(2, 8);          // = 256 - 2 to the power of 8
Math.sqrt(49);          // = 7 - square root
Math.abs(-3.14);        // = 3.14 - absolute, positive value
Math.ceil(3.14);        // = 4 - rounded up
Math.floor(3.99);       // = 3 - rounded down
Math.sin(0);            // = 0 - sine
Math.cos(Math.PI);      // OTHERS: tan, atan, asin, acos
Math.min(0, 3, -2, 2);  // = -2 - the lowest value
Math.max(0, 3, -2, 2);  // = 3 - the highest value
Math.log(1);            // = 0 natural logarithm
Math.exp(1);            // = 2.7182 pow(E,x)
Math.random();          // random number between 0 and 1
Math.floor(Math.random() * 5) + 1;  // random integer, from 1 to 5

var d = new Date();
Number(d);

Date("2017-06-23");                 // date declaration
Date("2017");                       // is set to Jan 01
Date("2017-06-23T12:00:00-09:45");  // date - time YYYY-MM-DDTHH:MM:SSZ
Date("June 23 2017");               // long date format
Date("Jun 23 2017 07:45:00 GMT+0100 (Tokyo Time)");

var d = new Date();
a = d.getDay();     // getting the weekday

getDate();          // day as a number (1-31)
getDay();           // weekday as a number (0-6)
getFullYear();      // four digit year (yyyy)
getHours();         // hour (0-23)
getMilliseconds();  // milliseconds (0-999)
getMinutes();       // minutes (0-59)
getMonth();         // month (0-11)
getSeconds();       // seconds (0-59)
getTime();          // milliseconds since 1970

var d = new Date();
d.setDate(d.getDate() + 7); // adds a week to a date

setDate();          // day as a number (1-31)
setFullYear();      // year (optionally month and day)
setHours();         // hour (0-23)
setMilliseconds();  // milliseconds (0-999)
setMinutes();       // minutes (0-59)
setMonth();         // month (0-11)
setSeconds();       // seconds (0-59)
setTime();          // milliseconds since 1970

var dogs = ["Bulldog", "Beagle", "Labrador"];
var dogs = new Array("Bulldog", "Beagle", "Labrador");

alert(dogs[1]);             // access value at index, first item being [0]
dogs[0] = "Bull Terier";    // change the first item

for (var i = 0; i < dogs.length; i++) {
  console.log(dogs[i]);
}

dogs.toString();                        // convert to string: "Bulldog,Beagle,Labrador"
dogs.join(" * ");                       // join: "Bulldog * Beagle * Labrador"
dogs.pop();                             // remove last element
dogs.push("Chihuahua");                 // add new element to the end
dogs[dogs.length] = "Chihuahua";        // the same as push
dogs.shift();                           // remove first element
dogs.unshift("Chihuahua");              // add new element to the beginning
delete dogs[0];                         // change element to undefined (not recommended)
dogs.splice(2, 0, "Pug", "Boxer");      // add elements (where, how many to remove, element list)
var animals = dogs.concat(cats, birds);  // join two arrays (dogs followed by cats and birds)
dogs.slice(1, 4);                        // elements from [1] to [4-1]
dogs.sort();                            // sort string alphabetically
dogs.reverse();                         // sort string in descending order
x.sort(function(a, b) { return a - b });   // numeric sort
x.sort(function(a, b) { return b - a });   // numeric descending sort
highest = x[0];                         // first item in sorted array is the lowest (or highest) value
x.sort(function(a, b) { return 0.5 - Math.random() }); // random order sort

eval();                     // executes a string as if it was script code
String(23);                 // return string from number
(23).toString();            // return string from number
Number("23");               // return number from string
decodeURI(enc);             // decode URI. Result: "my page.asp"
encodeURI(uri);             // encode URI. Result: "my%page.asp"
decodeURIComponent(enc);    // decode a URI component
encodeURIComponent(uri);    // encode a URI component
isFinite();                 // is variable a finite, legal number
isNaN();                    // is variable an illegal number
parseFloat();               // returns floating point number of string
parseInt();                 // parses a string and returns an integer

var a = str.search(/CheatSheet/i);

try {
  undefinedFunction();
} catch(err) {
  console.log(err.message);
}

throw "My error message";    // throw a text

var x = document.getElementById("mynum").value;
try {
  if (x == "") throw "empty";
  if (isNaN(x)) throw "not a number";
  x = Number(x);
  if (x > 10) throw "too high";
} catch(err) {
  document.write("Input is " + err);
  console.error(err);
} finally {
  document.write("<br />Done");
}

var str = '{"names":[' +
  '{"first":"Hakuna","lastN":"Matata" },' +
  '{"first":"Jane","lastN":"Doe" },' +
  '{"first":"Air","last":"Jordan" }]}';
obj = JSON.parse(str);
document.write(obj.names[1].first);

var myObj = { "name": "Jane", "age": 18, "city": "Chicago" };
var myJSON = JSON.stringify(myObj);
window.location = "demo.php?x=" + myJSON;

myObj = { "name": "Jane", "age": 18, "city": "Chicago" };
myJSON = JSON.stringify(myObj);
localStorage.setItem("testJSON", myJSON);

text = localStorage.getItem("testJSON");
obj = JSON.parse(text);
document.write(obj.name);

function sum(a, b) {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      if (typeof a !== "number" || typeof b !== "number") {
        return reject(new TypeError("Inputs must be numbers"));
      }
      resolve(a + b);
    }, 1000);
  });
}

var myPromise = sum(10, 5);
myPromise
  .then(function(result) {
    document.write(" 10 + 5: ", result);
    return sum(null, "foo");
  })
  .then(function() {})
  .catch(function(err) {
    console.error(err);
  });